…in, so use a custom cycle iterator instead

the environment is required for template compilation in caching loader

this required passing the origin to the non-debug parser too (i dunno
why this wasn't done before).

the loader directories stored in origin until this change weren't used anywhere,
and are still accessible in origin.loader.templateDirs - but the absolute file
path wasn't stored anywhere, but will be necessary for an upcoming change:
skipping the template containing an extends tag from extending itself.

this avoids re-parsing included templates in for loops

added a history array to context that contains the absolute paths
of all _extending_ templates. loaders need to check against
this array and exclude already used templates.

see dc50416#r50471128

using a regex instead of a string as first argument to replace, since
using a string would only replace the first occurrence